ENH: Add Remote Module for r/w of MGH files

The MGH file format is prevelant in many
neuroimaging environments and it would be
convenient if ITK were able to do at least
basic manipulations of these image file
formats.

This patch is intended to develop a solution
including MGHIO as a Remote Module.

The Remote Module has more extensive testing than the original.

Change-Id: I8d3e3d62062c2236e8aca5760551348c5eaf7494
Merge topic 'AddMGHImageIO'

5c7f10b ENH: Add Remote Module for r/w of MGH files